JPS5891080A - Hot press - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a hot press method for non-oxide ceramics. Specifically, when hot press sintering ceramic powder, it is necessary to improve the timing and application of pressure during sintering. By controlling the pressure arbitrarily, for example, by increasing the temperature without applying pressure, applying pressure at the beginning and end of the sintering process, and maintaining the unpressurized state in the middle, the incompatibility of crystal orientation can be eliminated. The present invention relates to a hot pressing method that makes it possible to obtain a sintered body.

Recently, ceramic materials, especially ceramics as heat-resistant materials, have been actively developed.

Among them, it is known that covalent compounds that are heat-resistant substances that are stable at high temperatures, particularly silicon nitride (Si3N4) and silicon carbide (SiC), are excellent materials.

Generally, ceramics are obtained by molding and sintering raw ceramic powder, but Si3N4. Unlike general oxide ceramics, SiC is a material that is difficult to sinter, so it is difficult to obtain a dense sintered body even if only a single composition, for example, Si3N4 powder is sintered.

Therefore, 5i5N4 powder contains MrO, At203, Y2
O5, CeO2.

Sintering is carried out by adding oxide powder such as BeO as a sintering aid.

As for sintering, normal sintering, reaction sintering, and hot press sintering are known, but the hot press sintering method, which sinters under pressure at high temperatures, produces a more dense sintered material. You can get a body.

However, this Hola l-press method requires a mold, and such a mold must be made of a material that has high temperature strength enough to withstand external pressure at high temperatures and can be processed into various shapes. From this point of view, carbon is preferably widely used.

On the other hand, even if hot pressing is carried out in this manner, this method has the disadvantage that anisotropy occurs in the vertical and horizontal directions of the sintered body. In other words, in the hot pre method, if the entire process is carried out under pressure, when grains try to grow at the sintering temperature, they are affected by the pressure and cannot grow in any direction, resulting in differences in strength in the vertical and horizontal directions. , the value is lower in the horizontal direction.

In view of the above points, the present inventors investigated a hot press method that allows grain growth in both the vertical and horizontal directions, and found that the pressure is temporarily stopped at the grain growth stage in hot press sintering. They solved the above-mentioned drawbacks and discovered scales that do not grow grains in any direction.

Hereinafter, a hot pressing method for ceramic powder containing Si3N4 powder as the main component will be explained based on the drawings.

First, an example of the pressurized state during sintering in the method of the present invention is as shown in FIG.

That is, (1) the temperature is raised without pressure to the softening temperature of the molded body, that is, the temperature at which sintering proceeds (for example, 1400°C or higher), and (2) the temperature is then raised while being raised or maintained at the sintering temperature. While pressurizing to 130-150 k2/αl, about 10-
Continue sintering for 20 minutes. At this stage, the particle spacing of the compact is reduced to facilitate sintering in the next stage. (Stage A) (3) After that, the pressure is released and the temperature is raised or sintered for about 30 to 40 minutes while maintaining it at the sintering temperature. Sintering is then performed with grain growth in free directions. . (B stage) (4) Next, apply a pressure of 180 to 200 kp/cJ and maintain the sintering temperature (e.g. 1700°C) for about 1
The sintering process is completed after sintering for 0 minutes. (C stage)
At this stage, the pores left in the sintered body at stages A and B are eliminated.

A sintered body without anisotropy can be obtained by going through the steps of A, B, and C.

The sintering steps A, B, and C do not necessarily require these three steps (in some cases, two steps A and B or two steps B and C are sufficient.

Next, this method will be explained using an example.

Example 1 5 wt% fvIy in Si3N4 powder with 90% a phase
After adding O powder and mixing and pulverizing with an attritor,
This pulverized material was used to form one side with a molding pressure of 5001c9/cy+ of 1ooIl+l+.

It was formed into a flat plate with a height of 40 m. Next, this compact was set in a carbon hot press mold, and hot press sintering was performed under nitrogen atmosphere under the same temperature and pressure conditions as shown in FIG.

As a comparative example, the same molded body was set in a carbon mold under the conditions shown in Fig. 2 under a nitrogen atmosphere, that is, at a pressure of 20
Hot press sintering was performed at 01 w/m and 1700° C. for 60 minutes.

Next, the obtained sintered body was sliced and subjected to a transverse rupture strength test in the direction in which it was pressed with a pot press and in the direction perpendicular thereto, and the results shown in Table 1 were obtained.

From this table, it can be seen that in the case of this example, there was almost no difference in strength depending on the pressing direction and the vertical direction.

This shows that the anisotropy of the sintered body is eliminated and a sintered body that is stable and high in strength in any direction can be obtained.

Table l Example 2 SiC powder to which 3% by weight of B4C powder was added was mixed and pulverized, and a molding pressure of 500 mm/crl was used to form a mold with a height of 4
It was molded into a 0 m flat plate.

Next, this molded body was set in a carbon mold, and the temperature was raised to 190°C (1°C) without pressure in a vacuum atmosphere, then the temperature was increased to 1900°C for about 10 minutes at 1501 w/ffl, and then The pressure was released and the temperature was raised to 2000°C, and the temperature was held for 40 minutes to allow grain growth in any direction to proceed with sintering, and then the temperature was kept at 2000°C for about 10 minutes under a pressure of 2001 w/ffl. Press sintering was performed.

As a comparative example, a molded body in the same carbon mold was subjected to hot press sintering at 200ψW and 2000°C for 50 minutes in a vacuum atmosphere.

When the obtained sintered body was sliced and the bending strength was measured in the direction in which it was pressed with a hot press and in the direction perpendicular to that direction, the results shown in Table 2 were obtained, indicating that the method of this invention is anisotropic. It has been demonstrated that this method is excellent in obtaining sintered bodies free of sintered bodies.

Table 2

[Brief explanation of the drawing]

Figure 1 shows the sintering time in the sintering process of the method of this invention;
A chart showing the relationship between temperature and pressure. FIG. 2 is a chart showing a similar relationship in the conventional method. Patent Applicant Sumitomo Electric Industries Co., Ltd. Agent Patent Attorney Kazu 1) Showa 7 - Figure 2 Hiran (Intermediate) Figure 2 Time 0 minutes) Continuation/Connection of Page 1 Akira 1-chome Konyo Kita, Komura Shuitan City No. 1-1 Sumitomo Electric Industries, Ltd. Itami Works

Claims (1)

[Claims] (11) A sintered body with no crystal orientation is obtained by arbitrarily controlling the timing and pressure of pressing during sintering when hot-press sintering ceramic powder. (2) Hot press sintering conditions include first raising the temperature without applying pressure, then applying pressure at the beginning and end of the sintering process, and maintaining the unpressurized state in the middle. A hot pressing method according to claim 1, characterized in that the ceramic powder has 5i5N4 as a main component.
Hot pressing method described in section. (4) The hot pressing method according to claim 1 or 2, wherein the ceramic powder contains SiC as a main component.